Silane modified diatomaceous earth mechanical insecticide

ABSTRACT

A mechanical insecticide is made by mixing water with at least one type of silane to make a silane solution which is then mixed with diatomaceous earth until there is substantial deposition of the silane material on the diatomaceous earth material, to make a silanized diatomaceous earth. The silanized diatomaceous earth can be diluted with water and applied to vertical and overhead surfaces using a sprayer, for the control of insects. The silanized diatomaceous earth can also be dried into a powder for broadcast application, or mixed as a paste for brush/roller/caulk application.

BACKGROUND OF THE INVENTION

Diatomaceous earth (DE) is a material predominately made up of thefossilized remains of diatoms, in particular the silica shell of diatomsknown as a frustule, which are naturally occurring depositscharacterized by lattice-like architectures. The physical structure offossil diatoms includes numerous pores that give the material a veryhigh surface pore volume and internal pore volume, contributing to thematerials outstanding absorptive quality. DE is mined from sedimentarydeposits and processed into a variety of grades useful in manyapplications. Such applications include filter material, abrasives,mechanical insecticide, cat litter, absorbents, chemical stabilizer (ex.nitroglycerin), and thermal insulator. Despite its many uses, there areconstraints that limit the applicability of diatomaceous earth. Forexample, water borne applications are generally not practical. Thematerial does not suspend in water or remain dispersed well enough forliquid spray application. Furthermore, prolonged storage in waterresults in compacted sediment that is difficult to re-suspend.

A well known use of DE is as a mechanical insecticide that killsnumerous different crawling insects. It is generally accepted that wheninsects crawl over or through dry DE powder they will suffer physicaldamage to their waxy epicuticle, and then the absorptive quality of DEextracts lipids from the insects body, causing a lethal dehydration.Unfortunately, reliable application of DE to surfaces where insectsoften crawl can be difficult because DE does not easily suspend in waterfor spray applications, and application of dry powder DE does not allowfor adequate coverage on vertical or overhead surfaces. DE is oftenapplied by pressurized air, which creates nuisance dust. Unmodified DEhas a high energy surface with numerous hydroxyl groups that hydrogenbond causing the material to become compact and claylike after settlingin aqueous medium. There is a need for a DE that forms a suspension inwater and has flow characteristics that make it amenable to sprayapplication to all surfaces where insects cause problems.

SUMMARY OF THE INVENTION

The present invention relates to diatomaceous earth (DE) reacted withsilanes. DE is modified by deposition of silanes to the DE substratesurface. Such modifications enhance or increase the functionality andapplicability of DE because it can then be mixed with water and sprayedonto practically any surface. Silylated DE is produced by reacting withsilanes of the formula R_(n)SiX_(4-n), wherein n is equal to 0-3, R isan organic functional group, and X is a hydrolyzable group. Silanes aresilicon chemicals that have a hydrolytically reactive center that canform stable covalent bonds with inorganic substrates. In addition, manysilanes can polymerize, enhancing coverage of substrates. Furthermoresilanes have an organic substitution that alters the properties of thesubstrate, making it suitable for a variety of physical interactions.Silylated DE, which has improved aqueous dispersion and suspension, canbe used as an improved mechanical insecticide that can be applied byspraying a solution of silylated DE and water.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is diatomaceous earth that has been modified whensilanes form covalent bonds with the surface of diatomaceous earth andmetal oxides naturally present in the material. It is the object of thisdisclosure to detail methods for modifying diatomaceous earth (DE) withsilanes by deposition of one or more silanes or a combination ofsilanes. There are constraints of unmodified DE that can be overcome bymodification with silanes such that the modified DE imparts novel anduseful characteristics to the material.

This objective can be achieved by reacting the material with silanes ofthe formula R_(n)SiX_(4-n), wherein n is equal to 0-3; preferably 0-2,more preferably, 1-2, most preferably 1, R is an organic functionalgroup, and X is a hydrolyzable group. R groups can be methyl, linearalkyl, branched alkyl, aryl, etc. X can be hydrolysable groups such aschloro, alkoxy, amine/silazane, silanol, acetoxy, amine, dimethylamine,oxime, etc.

Silanes that alter the surface energy of a substrate without impartingchemical reactivity are referred to as non-functional silanes.Non-functional silanes fall into two classes, hydrophobic silanes andhydrophilic silanes. Hydrophobic non-functional silanes have organicsubstitutions such as; methyl, linear alkyl, branched alkyl, fluorinatedalkyl, aryl, etc. Hydrophilic non-functional silanes have organicsubstitutions that are polar, hydroxylic, ionic, and charge inducible,etc.

Modification by non-functional silanes imparts a variety of usefulproperties to substrates. Such properties are hydrophobic, hydrophilic,lipophobic, lipophilic, oleophobic, oleophylic, charge conducting,ionic, release, etc. This has made silanized materials useful in a widerange of application such as; low energy coatings, pigment dispersants,water repellents, chromatography, conductive coatings, and antimicrobialcoatings.

Excellent substrates for silanes include silica, quarts, glass, andstable metal oxides. These substrate have adequate hydroxyl groups (—OH)for deposition of silanes. Diatomaceous earth would likewise be asuitable substrate for silanization as it typically consists of 80-90%silica and roughly 5% stable metal oxides.

Moisture absorption and retention negatively impacts finer grades of DEused as insecticide. The cohesiveness of water causes DE particles tostick together in a fashion that alters the consistency of the material.As the material becomes coarser, fewer particles are able to attach toinsects that crawl over or through the material.

Modification to diatomaceous earth can also be achieved by deposition ofdipodal silanes of the formula X₃Si—(CH₂)_(n)—R—(CH₂)—SiX₃, wherein R isan organic functional group covalently bonded to both silyl groups, X isa hydrolyzable group. R groups can be alkyl, aryl, etc. X can behydrolysable groups such as chloro, alkoxy, amine/silazane, silanol,acetoxy, amine, dimethylamine, oxime, etc.

Dipodal silanes are also useful for surface modification of diatomaceousearth. Dipodal silanes have the following chemical structure where X isa hydrolysable group and R is an organofunctional group:

We have treated diatomaceous earth with a variety of silanes includingorganosilanes with organic substitutions that are hydrophobic,hydrophilic, and hydrophobic with embedded hydrophilicity. In generalall varieties have shown some ability to improve diatomaceous earth asan insecticide. Thus far, of those we have tested, silanes with anorganic substitution that can form hydrophobic phases with embeddedhydrophylicity performed the best. This included3-(trimethoxysilyl)propyldimethyl-octadecyl ammonium chloride;Hexadecyltrimethoxysilane, N,N-dioctyl-N′-triethoxysilyl proplyllurea;and Trimethoxysilylpropyl-N,N,N-tri-n-butlyammonium bromide. Ofparticular value is the silane3-(trimethoxysilyl)propyldimethyl-octadecyl ammonium chloride (alsoknown as Octadecyldimethyl (3-trimethoxypropyl)ammonium chloride). Itperformed the best in insecticidal trial and also formulates the best inwater, producing sprayable dispersions.

Applying Silanes—Methods of Deposition

The degree of silylation is dependent on the quantity of silane used ina particular reaction. Typically enough silane is added to assuremonolayer deposition on the substrate; though less can be used forpartial deposition and more for polylayer deposition. Polylayerdeposition is also dependent on the type of silane. Silanes with threehydrolysable groups are most capable of polylayer deposition since,after initial deposition, they have free hydolyzable groups that canpolymerize with silane monomers.

Estimates for Silane Loading on DE Particles

Particle Size *Amount of Silane <1 micron 1.5% 1-10 microns 1.0% 10-20microns 0.75%  >100 microns 0.1% *minimum of monolayer coverageDeposition from Aqueous Alcohol Solutions

Deposition of silane from aqueous alcohol solution is advantageous forproducing dry DE products as volatile alcohols are easily removed byheat drying, evaporation, and/or vacuum. In addition, aqueous alcoholsolution can dissolve water insoluble silanes.

The following method can be used for silylaton of diatomaceous earth: Anaqueous alcohol solution is adjusted to pH 4.5-5.5 (typically withacetic acid). Silane is added to the solution and completely dissolvedwith stirring (silane concentration is dependant on the the particlesize and amount of material to be silylated, in addition the volume ofsilylating solution has to be considered). Diatomaceous earth is addedto the solution and mixed by stirring to assure even deposition on thesubstrate. Approximately ten minutes is allowed for silanol formationand deposition. The modified DE is cured by heating for 5-10 minutes at110° C. or 24 hours at room temperature (<60% humidity). The materialcan be dried by low heat, evaporation or vacuum.

For the above procedure enough solution should be added to completelywet the substrate material, but excessive amounts are not necessary. Inaddition the solution should carry enough silane to attain the desireddegree of deposition. Furthermore mixing speed should be adequate toprevent uneven deposition on the substrate.

Generally the following ranges can be used for preparing the aqueousalcohol solution to be used for silylation of DE. The ranges are inweight percent:

Formulation Range of Aqueous Alcohol Solution

Ingredient Operating Range Preferred Range Alcohol 5-95 90-94.8 Water5-95 5-9.8 Acid Quantity sufficient <0.1 to adjust pH 4.5-5.5 SilaneQuantity sufficient 0.1-4.9  to achieve desired degree of deposition

The following alcohols are preferred: ethyl, propyl and isopropyl. Thefollowing acids are preferred for adjusting pH: acetic.

Deposition from Aqueous Solution

Silane deposition from aqueous solution is preferred for producingliquid suspension, slurry, and gel of diatomaceous earth. Depositionfrom aqueous solution can be performed in the following manner: Silaneis completely dissolved in water with mixing (the concentration useddepends on the amount of substrate and degree of deposition, also thevolume of water is considered). Insoluble silanes can be emulsifiedusing nonionic surfactant. Diatomaceous earth is added with mixing.Mixing is continued for up to 10 minutes to assure even deposition onthe substrate. Mild heating 40-70° C. for 10-30 minutes can acceleratedeposition, however deposition at room temperature will occur.

Deposition Using Chlorosilanes in Anhydrous Alcohols

EXAMPLE 1

Preparation of silylated diatomaceous earth from aqueous solution. A1000 gram (approximately 1 liter) solution was prepared in accordancewith the present invention by mixing the following ingredients:

Ingredient Weight Percent (%) Grams (g) Water 87.875 878.75 Acid 0.0250.25 3-(trimethoxysilyl)propyldimethyl- 0.1000 1.0 octadecyl ammoniumchloride DE 12.000 120.0 Totals 100.000 1000.00

This formulation produces a suspension of 1-10 micron DE (unmodified)particles in aqueous medium. The particles will settle in the solutionbut remain loose and semi-dispersed. Untreated DE forms a sediment layerthat becomes compact and will not suspend without vigorous and prolongedagitation.

Our invention remains dispersed and free flowing in the liquid phase andcan be applied as a liquid spray. Modified DE is compatible with avariety of spray devices or technologies-trigger sprayers, pumpsprayers, compressed liquid sprayers, electrostatic sprayers, airlesssprayers, etc.

Research has shown an inversely proportional relationship between DEeffectiveness and atmospheric humidity. Effectiveness decreases withincreasing humidity. Atmospheric humidity could reduce the potential forinsects to dehydrate, however; our research also indicates thatatmospheric moisture negatively impacts DE. Absorbed moisture increasescohesion between particles due to hydrogen bonding between surfacehydroxyl groups and water molecules. The effect of hydrogen bonding isto increase stiction (static friction) between particles. Stictioninhibits transfer of particles to insects that pass over or throughdiatomaceous earth.

Even without moisture there are still cohesive forces between particlesof diatomaceous earth due to hydrogen bonding between surface hydroxylgroups of adjacent particles. Reducing the number of free hydroxylgroups would reduce the cohesive forces that affect transfer of DEparticles to the surface of insects crawling over or through thematerial.

Needed is DE with fewer hydroxyl groups that create cohesive forces.Treatment with silanes reduces free hydroxyl groups. With fewer hydroxylgroups our invention is able to be formulated with water and is able tobe applied as a mixture in the water phase. It recovers well afterapplication in the aqueous phase and is more dry and powdery thanunmodified DE. In addition by lowering static friction throughquantitative reduction of free hydroxyl groups, it is better able toattach to insects that crawl over or through the material.

The invention, like traditional DE, can be used as a powder forbroadcast application or mixing with grains, and there are severalimprovements over the current state of the art:

-   -   1. Silane modified DE is dispersable in water and can be        formulated for liquid spray application.    -   2. Silane modified DE is more active and kills insects faster        than natural or unmodified DE.    -   3. Silane modified DE resist negative impact of water whether        absorbed after contact or from atmospheric humidity.    -   4. Silane modified DE is able to be used with natural and        synthetic pyrethrins; and potentially is a better carrier of        pyrethrins.    -   5. Because 3-(trimethoxysilyl)propyldimethyl-octadecyl ammonium        chloride in an antimicrobial, silanes modified with it may also        have antimicrobial properties. Grains, plants, fruits,        vegetables and other perishables treated for insects may also be        resistant to attack from bacteria and fungi.

Like natural unmodified DE, silane modified DE can potentially beconsidered inert as non-functional silanes of this invention arepermanently bonded to the surface of DE.

The preferred silane of this invention,3-(trimethoxysilyl)propyldimethyl-octadecyl ammonium chloride, consistsof a relatively large lipophyllic hydrocarbon tail that would promoteadsorption of the waxy cuticle that protects insects. In addition thecationic group of this same silane is hydrophilic and would promoteadsorption of water and potentially accelerate dehydration of insects.We have treated DE with other organosilanes possess a hydrophobicsubstitution with embedded hydrophilicity that have also shown increasedinsecticidal rate. The invention is made by deposition of silane on thesurface of diatomaceous earth. Three deposition reactions arepreferable: 1) deposition from aqueous solution 2) deposition fromaqueous-alcohol solution and 3) bulk deposition. Other known depositionreactions may be substituted, but may be less practical.

Deposition from aqueous solution is preferred for making solutions wherethe invention will remain in the liquid phase to be applied as liquidspray. Deposition from aqueous-alcohol solution is preferred for makingdry material since volatile alcohols are easily removed by heat,evaporation, and vacuum distilation. Bulk deposition is also preferredfor producing dry material.

For the invention, the degree of deposition ranges from 1 part silane to50-2000 parts DE by weight (1:50-1:2000, silane:DE). Preferred for theinvention is 1:100-500 silane:DE by weight.

Deposition form aqueous solution. Producing silane modified DE is asimple matter of adding DE to a silanating solution containing aquantity of silane sufficient to achieve the desired degree ofdeposition. Temperature and pH ranges are not given here. The optimumfor pH is typically 4.0-5.0. Range of ingredients of the silane solutionis as follows (figures are weight percent of total aqueous solution)

Formulation Range for Aqueous Silane Solution (Silanating Silution).

Ingredient Operating Range Preferred Range Water 80.0-99.99 98.0-99.90Silane 0.01-20.0  0.1-2.0 DE is added to the silane solution at the following ranges (in weightpercent)Formulation Range for making Silane Modified DE in Aqueous Solution

Ingredient Range Preferred Range Silane Solution* 50-99 65-99 DE  1-50 1-35 *The concentration of silane is dependent on the degree ofdeposition requiredThe above ranges produce viscous pastes or slurries to low viscosityaqueous dispersions or suspensions, which are suitable for directapplication using a roller, brush, caulk gun or other application methodcommonly used for paints.

Deposition form aqueous alcohol solution. DE can be modified by mixingin an aqueous alcohol solution. The procedure requires preparation of anaqueous alcohol solution ranging from 10-95% alcohol, 95% preferred.Enough silane is added to give the desired degree of deposition. Thetable below gives formulation ranges for the silanating solution (rangesare expressed as weight percent). Temperature and pH ranges are notgiven here. The optimum for pH is typically 4.0-5.0.

Formulation Range Aqueous Alcohol Solution (Silanating Solution).

Ingredient Operating Range Preferred Range Aqueous-alcohol solution* 80.0-99.99  97.8-99.80 Silane 0.01-20.0 0.1-2.0 *Aqueous-alcoholsolution range is 10-95% in water

DE is added to the silane solution at the following ranges (in weightpercent)

Formulation Range for Making Silane Modified DE using Aqueous AlcoholSolution

Ingredient Range Preferred Range Silane Solution* 50-99 65-75 DE  1-5025-35 *The concentration of silane is dependent on the degree ofdeposition requiredAfter thorough mixing, alcohol can be removed by evaporation at roomtemperature or with heat. Alcohol can also be removed by vacuumdistillation methods as well. Heating will help cure the silane layer.

Modification of DE by aqueous solutions produce pastes, slurries anddispersions (suspension) of the material. Paste and slurries can be usedas they are or used as concentrates to make liquid dispersion. Theliquid dispersions made by this method flow freely and are amenable tospray application. Even after settling the material can be re-suspendedeasily with light to moderate agitation.

Modified DE produced from reaction in aqueous medium can be dried andprocessed into powder if needed. If producing a dry product or powder,modified DE made using aqueous alcohol solution is more suitable asvolatile alcohols are more easily removed by evaporation. DE modifiedwith silanes from reaction in aqueous alcohol solution when rehydratedshow characteristics similar to the material when made in aqueoussolution.

Several types of silanes have shown the ability to modify DE withpositive results. In particular the silane3-(trimethoxysilyl)propyldimethyl-octadecyl ammonium chloride displaysthe best results for dispersion in water and for insecticidal activity.

Results of Insecticidal trial: Modified DE kills insect faster thanunmodified DE of the same origin. The table below shows testing results.For the test below 10% liquid suspensions of DE were mixed with highagitation and quickly poured into Petri dishes. Excess DE was poured offand the material coating the Petri dishes was allowed to dry. Afterdrying, beetles were placed in the dishes and monitored for kill time.

Insecticidal Trial Results for Darkling Beetle

Modified^(b) DE (weight ratio silane:DE) DE Compositions: ^(a)DE(unmodified) 1:100 1:150 1:250 Average Kill Time (hours): 94 36 36 34^(a)natural diatomaceous earth, 10-50 micron particle size, averagesurface area 69 m²g⁻¹ ^(b)modified with3-(trimethoxysilyl)propyldimethyl-octadecyl ammonium chloride

One obvious trait of silane modified DE was that more of it attaches toinsects as they crawl over the material when compared to unmodified DE.This was true of all the types of silanes tested and hints that part ofthe insecticidal activity of silane modified DE is due to reduction offree hydroxyl groups on the surface of DE. Hydroxyl groups may causecohesion that prevents DE particles from attaching to insects that crawlover it. Noteworthy is that silane modified DE is softer and morepowdery whereas unmodified DE is more gritty and crystalline.

Other silanes were used to modify DE. These were chosen for havingproperties of hydrophobic or hydrophyllic or both. While theydemonstrated increase insecticidal activity over unmodified DE they werenot as effective as 3-(trimethoxysilyl)propyldimethyl-octadecyl ammoniumchloride. They also were not as proficient at suspending DE particles inaqueous medium. They did however show an increase in particles attachedto insects when tested as described above. This indicates that silanemodification of DE in general increases insecticidal activity, possiblythrough reduction of free hydroxyl groups as described above.

While a preferred form of the invention has been shown and described, itwill be realized that alterations and modifications may be made theretowithout departing from the scope of the following claims.

What is claimed is:
 1. A method for making a mechanical insecticidecharacterized by the steps of: mixing water with at least one type ofsilane to make a silane solution, wherein the type of silane is one withwhich an organic substitution can form hydrophobic phases with embeddedhydrophylicity; and mixing natural uncalcined diatomaceous earth withthe silane solution, wherein the diatomaceous earth has an averageparticle size of between 1 and 20 microns, until there is substantialdeposition of the silane material on the diatomaceous earth material, tomake a silanized diatomaceous earth; and wherein not adding a pestcontrol agent to the mechanical insecticide.
 2. The method of claim 1further comprising the step of mixing the silanized diatomaceous earthwith additional water to provide a fluid suspension; and wherein thestep of applying the silanized diatomaceous earth is characterized byspraying the fluid suspension through a sprayer.
 3. The method of claim2 wherein the step of spraying is characterized by spraying the fluidonto vertical and overhead structures.
 4. The method of claim 1 whereinthe step of mixing water with at least one type of silane is furthercharacterized by adding an alcohol to the mixture to make the silanesolution.
 5. The method of claim 4 further comprising the step ofremoving the alcohol from the silanized diatomaceous earth to produce adry powder.
 6. The method of claim 1 wherein the ratio of silane todiatomaceous earth is in the range of 1:50 and 1:2000 by weight.
 7. Themethod of claim 1 wherein the ratio of silane solution to diatomaceousearth is in the range of 1:1 and 1:100 by weight.
 8. The method of claim1 further comprising the step of adjusting the pH level of the silanesolution to between 4.0 and 5.5.
 9. The method of claim 8 wherein thestep of adjusting the pH level is characterized by adding acetic acid.10. The method of claim 1 further comprising the step of heating thesilane solution to accelerate deposition on the diatomaceous earth. 11.The method of claim 1 wherein the type of silane is of the formulaR_(n)SiX_(4-n), wherein n is equal to 0-3, R is an organic functionalgroup, and X is a hydrolyzable group.
 12. The method of claim 1 whereinthe type of silane is of the formula X₃Si—(CH₂)_(n)—R—(CH₂)—SiX₃,wherein R is an organic functional group covalently bonded to both silylgroups, and X is a hydrolyzable group.
 13. The method of claim 1 whereinthe type of silane is 3-(trimethoxysilyl) propyldimethyl-octadecylammonium chloride.
 14. The method of claim 1 wherein the amount ofsilane is adequate to assure monolayer deposition on the diatomaceousearth substrate.
 15. The method of claim 1 wherein the ratio of silaneto diatomaceous earth is between 1:50 and 1:200 by weight.
 16. Themethod of claim 1 wherein the diatomaceous earth has an average particlesize greater than 20 microns; and wherein the ratio of silane todiatomaceous earth is between 1:100 and 1:1500 by weight.
 17. The methodof claim 1 wherein the diatomaceous earth has an average particle sizeless than 1 micron; and wherein the ratio of silane to diatomaceousearth is between 1:5 and 1:100 by weight.
 18. The method of claim 1wherein the type of silane is one with which an organic substitution canform hydrophobic phases with embedded hydrophylicity.
 19. The method ofclaim 1 wherein the type of silane is insoluble; further comprising thestep of emulsifying the silane using nonionic surfactant.